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  Autofocus actuatorRelated Patent Categories: Dynamic Information Storage Or Retrieval, With Servo Positioning Of Transducer Assembly Over Track Combined With Information Signal Processing, Optical Servo System, Optical Head Servo System StructureThe Patent Description & Claims data below is from USPTO Patent Application 20060028929. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an autofocus actuator, and more specifically to an autofocus actuator that can be employed in digital cameras or other small-sized electronic apparatuses equipped with a camera, e.g., cellular phones. [0003] 2. Description of the Related Art [0004] In digital cameras, an actuator that can displace a lens in an optical axis direction is employed for the sake of autofocusing and zooming operations. This type of actuator is adapted to displace the lens in the optical axis direction by virtue of an interaction between the magnetic field generated by the electricity flowing through a coil and the magnetic field of a permanent magnet. In recent years, a need exists for the function of autofocus even in a camera mounted to cellular phones, because the number of pixels of a picture-taking element for use in the cellular phone camera tends to increase up to the order of mega pixels greater than one million. [0005] One example of conventional autofocus actuators is disclosed in Japanese Patent Laid-open Publication No. 2003-295033. This autofocus actuator is comprised of a front lens, a front support frame for supporting the front lens, a front coil attached to the front support frame, a front spring affixed to the front support frame, a rear lens, a rear support frame for supporting the rear lens, a rear coil attached to the rear support frame, a rear spring affixed to the rear support frame, a magnet, a magnet support member and a yoke. The front coil is disposed in the outer gap between the magnet and the yoke, while the rear coil is located in the inner gap between the magnet and the yoke. Applying electric current to the front coil enables the front lens to move into a position where the front lens keeps in balance with the resilient force of the front spring. Likewise, applying electric current to the rear coil can bring the rear lens into a position where the rear lens keeps in balance with the resilient force of the rear spring. [0006] According to the conventional actuator described above, magnetic flux is leaked out from the permanent magnets at the surfaces thereof which are opposite to the surfaces thereof in contact with the yoke, that is from an open side of the yoke. Therefore, magnetic fields in the outer gap and the inner gap between the magnets and the yoke become smaller, which leads to a problem in that the driving force of the front support flame and the rear support flame in which the lenses are mounted is decreased. SUMMARY OF THE INVENTION [0007] With the above-mentioned problems in mind, it is an object of the present invention to provide an autofocus actuator that can prevent a leakage of the magnetic flux in the yoke, whereby enabling to enhance the driving force of the holder in which lenses are mounted. [0008] In order to achieve the above object, the present invention is directed to an autofocus actuator which comprises: a holder having a hollow body portion having one end to which a lens is mounted; a coil fixedly secured to the holder in such a manner as to surround the hollow body portion of the holder; a pair of leaf springs respectively provided on opposite end sides of the hollow body portion of the holder for supporting the holder displaceably in an optical axis direction of the lens with the holder being positioned in a radial direction; a yoke having a plurality of permanent magnets provided in a confronting relationship with the coil, the yoke adapted to adjust the position of the lens attached to the holder in the optical axis through the use of interaction between a magnetic field of the permanent magnet and a magnetic field generated by the coil as the coil is supplied with electric power, and means provided in the yoke for preventing leakage of magnetic flux from the plurality of permanent magnets. [0009] According to the present invention, it is preferred that the magnetic flux leakage preventing means includes a magnetic member disposed on the permanent magnets so as to interconnect the permanent magnets in such a condition that the magnetic member is kept in contact with the surfaces of the permanent magnets. [0010] With the autofocus actuator of the present invention constructed as above, a leakage of the magnetic flux from the permanent magnets at the open side of the yoke can be suppressed by the magnetic member provided in the yoke. Accordingly, the magnetic field that is directed from the permanent magnets toward the inner cylindrical portion of the yoke is increased, whereby enabling to enhance the driving force of the holder. [0011] According to the present invention, it is also preferred that the outer cylindrical portion is formed into a generally cylindrical shape, and the permanent magnets are arcuate permanent magnets arranged along the magnet mounting surface of the outer cylindrical portion, wherein the magnetic member is formed into a ring shape which is disposed to interconnect the permanent magnets in such a condition that the ring-shaped magnetic member is kept in contact with the end surfaces of the permanent magnets that are opposite to the end surfaces thereof in contact with the connecting portion of the yoke. [0012] This makes sure that the magnetic member can be readily produced through an integral forming process. [0013] According to the present invention, it is also preferred that the width of the ring-shaped magnetic member in a radial direction thereof is substantially the same as the thickness of each permanent magnet. [0014] This allows the coil to be disposed in the yoke with no hindrance, thus making it possible to sufficiently reduce the amount of the magnetic flux which would be leaked out. [0015] According to the present invention, it is also preferred that the ring-shaped magnetic member has such a thickness that a surface thereof which is opposite to other surface thereof in contact with the permanent magnets is located at a position backed toward the connecting portion of the yoke from the end surface of the outer cylindrical portion. [0016] This permits the leaf spring to be attached to the end surface of the yoke with no hindrance. [0017] Further, another aspect of the present invention is directed to an autofocus actuator, which comprises: a holder including a hollow body portion having one end to which a lens is attached, and a flange portion provided along the perimeter of the other end of the hollow body portion; a coil fixedly secured to the flange portion of the holder in such a manner as to surround the hollow body portion of the holder; a yoke including an inner cylindrical portion having an insertion bore into which the hollow body portion of the holder is inserted and an outer cylindrical portion provided outside of the inner cylindrical portion with a predetermined spacing left therebetween through a connecting portion so that the coil is accommodated within the predetermined space; a plurality of permanent magnets disposed on a magnet mounting surface which is an inner circumferential surface of the outer cylindrical portion of the yoke; a pair of leaf springs provided on opposite end sides in an optical axis direction of the hollow body portion for supporting the holder displaceably in the optical axis direction with the holder being positioned in a radial direction thereof; and a pair of support frames respectively provided outside of the pair of leaf springs along the optical axis direction and adapted to sandwichedly support the leaf springs between the opposite end surfaces of the yoke and the support frames, respectively, each of the support frames having an opening formed at least on a part that corresponds to the lens attached to the holder, in which the position of the holder in the optical axis direction is displaceably adjusted by flowing a current to the coil, wherein the autofocus actuator further comprises means for preventing leakage of magnetic flux from the plurality of permanent magnets. [0018] With the autofocus actuator of the present invention constructed as above, a leakage of the magnetic flux from the permanent magnets at the open side of the yoke can be suppressed by the magnetic member provided in the yoke. Accordingly, the magnetic field that is directed from the permanent magnets toward the inner cylindrical portion of the yoke is increased, whereby enabling to enhance the driving force of the holder. [0019] The above and other objects and features of the invention will become more apparent from the following detailed description when the same is read in conjunction with the accompanying drawings that are presented for the purpose of illustration only. BRIEF DESCRIPTION OF THE DRAWINGS [0020] FIG. 1 is a perspective view showing the external appearance of an autofocus actuator proposed by the inventor of the present invention; [0021] FIG. 2 is an exploded perspective view of the autofocus actuator shown in FIG. 1; Continue reading... Full patent description for Autofocus actuator Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Autofocus actuator patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Autofocus actuator or other areas of interest. ### Previous Patent Application: Optical element, optical head, optical recording reproducing apparatus and optical recording/ reproducing method Next Patent Application: Optical disk apparatus with objective lens protective unit Industry Class: Dynamic information storage or retrieval ### FreshPatents.com Support Thank you for viewing the Autofocus actuator patent info. 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